1. Field of the Invention
The present invention relates in general to a producing system and method of microporous laminated sheets, and microporous laminated sheets produced thereby. More particularly, it relates to a producing system and method of microporous laminates capable of maintaining and improving a breathability of a microporous film while maintaining an excellent adhesion between the microporous film and a non-woven fabric web, and to microporous laminated sheets produced thereby.
2. Description of the Prior Art
As articles permeable to air but impervious to liquids such as water, microporous laminated sheets are generally used. Such microporous laminates have utilities, for example, in disposable articles, such as work-wears to be worn by workers in various working places, infant and senile diapers, feminine sanitary napkins and the like, materials for preventing freezing of a wall or roof, packing materials of fluffs of winter clothes, packing materials for the coloring improvement into a uniform color, for the sugar degree improvement or for the prevention of damages by blight and harmful insects, in fruits or fruit crops, or other industrial applications.
FIG. 1 shows a disposable work-wear 1. In FIG. 1, a non-woven fabric 2 constituting an inner layer of the work-wear 1, and a microporous film 3 bonded to the non-woven fabric 12 are formed of such microporous laminates. Of course, the microporous film 3 has a plurality of microvoids formed therein so that it is permeable to air but is impervious to liquids such as sweat or water.
In such microporous laminates, there is used a microporous film pressure-stretched by a stretching section (as shown in FIG. 2) in a microporous film-producing section. The stretching section generally includes a plurality of base rollers 6 through which the microporous film is transported in contact. Also, it includes pressing rollers 7 for pressing the microporous film 3 passing over the respective base rollers 6. Here, the base rollers are coated with chrome, and the pressing rollers 7 are generally formed of an EPM- or EPDM-based material. The respective base rollers 6 are rotated at a speed different from each other and have a faster rotation speed at the input portion of the microporous film than at the output portion. For this reason, the microporous film can be pressed while being transported, thereby being stretched.
However, the stretching section in such a microporous film-producing system is disadvantageous in that it makes a width of the narrow microporous narrow, and also results in a difference in thickness and physical property between the center portion and the edge portion of the microporous film. Also, the stretching section is impossible to control batch wise the pressure and the rotation speed, so that the sliding of the microporous film occurs. This results in the occurrence of a non-stretched portion in the microporous film and results in a disproportion in the microporous film thickness.
Meanwhile, one of prior methods of making the laminated sheets as described above is disclosed in European Patent Publication 0 309 073 A2. According to the method disclosed in this patent, an HDPE-based, mesh-shaped clothes is used as a reinforcement (i.e., a non-woven fabric web), and the microporous film is integrated in the reinforcement by using a heating-pressing manner to form a microporous laminated sheet. In such a method of laminating the microporous film to the HDPE mesh as the reinforcing material by heating pressing, the microporous film which is based on LDPE and LLDPE has a melting point of about 110xc2x0 C. to 125xc2x0 C., whereas the non-woven fabric web which is based on HDPE is about 125xc2x0 C. to 135xc2x0 C. Accordingly, as the microporous film and the non-woven fabric web have the different melting point, a temperature at which they are laminated to each other needs to be increased to the highest melting point. Where the laminating temperature is increased as such, microvoids of a several xcexcm to several tens xcexcm size formed in the microporous film are closed due to the high temperature and pressure applied to the microporous film. For this reason, it has problems in that the breathability is significantly decreased or lost and the laminated sheet is very stiff. As a result, the microporous laminated sheets produced by the heating pressing method have a poor product quality and are unsuitable for use in a work-wear requiring a particularly excellent breathability, such as an industrial dust-proof wear.
Meanwhile, Japanese Patent Publication No. 10511318 discloses a producing method of a microporous laminated sheet for a business work-wear. In this method, a solid adhesive, called the hot melt, which is based on EVA (ethylene vinyl acetic acid) or polyolefin, is melted using an applicator named the hot-melt applicator so as to be converted into the emulsion state. The resulting adhesive is spray applied onto the microporous film or the non-woven fabric as the reinforcement in a melt spraying manner, after which the microporous film or the non-woven fabric are laminated to each other, forming a laminated sheet.
However, in such a laminating method, when the adhesive melted to a desired temperature is spray applied on the surface of the microporous film by the applicator, the adhesive is partially non-uniformly applied. Thus, the adhesion is also partially different throughout the applied surface, so that the uniform adhesion throughout the applied surface is not provided. In addition to this problem, the adhesive is not uniformly applied throughout the surface at a uniform amount when spraying. Thus, at portions which lacks the adhesive, the isolated adhesive portions occur, whereas at portions on which the adhesive is excessively applied, pores in the microporous film are closed with the adhesive to decrease the breathability and also the adhesive is consumed excessively. Furthermore, because of these problems, in the case of the industrial work-wear requiring the launderability, there is resulted in the diffusion of water due to the partial delamination, such that the non-woven fabric and the microporous film are easily separated from each other.
Moreover, in preparing the microporous film, the stretching method employing a change in the linear-velocity of mirror roller plated with chrome is used mainly for the stretching of common polyethylene films having a narrow width. Where this method is applied for the stretching of the microporous film, however, the width of the microporous film to be prepared become very narrow, and also a difference in thickness and physical property between the edge portion and center portion of the film are caused. Additionally, when stretching the microporous film having a wide width in the range of, for example, from 2,000 nm to 3,000 nm, a partial stretching deviation is often caused. This adversely affects the production of a microporous film having an excellent mechanical strength and an excellent and uniform breathability.
It is therefore a major object of the present invention to provide a system for making a laminated sheet, which allows a breathability of microporous film to be maintained or improved while making an adhesion between the microporous film and reinforcement excellent.
It is other major object of the present invention to provide a method for making a laminated sheet, which allows a breathability of microporous film to be maintained or improved while making an adhesion between the microporous film and the reinforcement excellent.
It is another major object of the present invention to provide a laminated sheet, which has a maintained or improved breathability of microporous film while having an excellent adhesion between the microporous film and the reinforcement.
It is also another major object of the present invention to provide a microporous film-producing system, which includes a stretching section of capable pressing a microporous film to have a generally uniform thickness.
It is still object of the present invention to provide a system and method for making a laminated sheet, which allows a bonding portion between the microporous film and the reinforcement generally uniform and which can prevent an excessive consumption of the adhesive. Also, it is an object of the present invention to provide a laminated sheet produced by these system and method.
It is yet another object of the present invention to provide a system and method for making a laminated sheet using an applying means capable of applying an adhesive uniformly throughout a bond surface of the microporous film and/or the reinforcement. Also, it is an object of the present invention to provide a laminated sheet produced by these system and method.
It is further another object of the present invention to provide a laminated sheet-producing system and method of capable applying a generally uniform pressure to a laminated sheet, and a laminated sheet produced thereby.
The above objects can be achieved by a microporous laminated sheet-producing system for bonding a microporous film to a reinforcement, which comprises a microporous film-feeding section serving to feed the microporous film; a reinforcement-feeding section around which the reinforcement to be bonded to the microporous film is wound unwindably; an adhesive-applying section serving to apply an adhesive in a linear or lattice shape, on the microporous film fed from the microporous film-feeding section; a drying chamber serving to dry the microporous film applied with the adhesive; a laminating section serving to bond the microporous film discharged from the drying chamber and the reinforcement to each other; and a winding section to collect a laminated sheet from the laminating section.
Also, the above objects can be achieved by a microporous laminated sheet-producing method for bonding a microporous film to a reinforcement, which comprises the steps of: feeding a microporous film; feeding a reinforcement to be bonded to one side of the microporous film; applying an adhesive on the microporous film in a linear or lattice shape; drying the microporous film applied with the adhesive; bonding adhesively the reinforcement to one side of the dried microporous film to form a laminated sheet; and winding the laminated sheet.
Also, the above objects can be achieved by a microporous laminated sheet which comprises a microporous film formed from a resin composition comprising 30 to 70% by weight of a polyolefin resin, 1 to 70% by weight of alpha-olefin copolymer, and 20 to 70% by weight of an inorganic filler; a polypropylene-based reinforcement bonded to one side of the microporous film and serving to reinforce the microporous film; and an adhesive interposed between the microporous film and the reinforcement in a linear or lattice shape and serving to bond the microporous film and the reinforcement to each other.